Soap gel based glue stick

ABSTRACT

Adhesive sticks are obtained using water-based preparations of synthetic polymers of adhesive character and soaps which act as shaping gel-forming components. Mixtures of polyurethanes and polyvinyl pyrrolidone are used as the synthetic polymers. The polyurethane may be in the form of a dispersion and produced by reacting at least one polyol, at least one polyfunctional isocyanate and a component capable of salt formation in alkaline aqueous solution and/or a nonionic hydrophilic modifying agent.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an adhesive stick produced from a water-basedpreparation of a synthetic polymer of adhesive character and a soap gelas the shaping gel-forming component and, optionally, other auxiliaries.The invention also relates to a process for the production of suchsticks and to their use.

2. Discussion of the Related Art

Adhesive sticks (=dimensionally stable stick-like adhesives which leavebehind a tacky film when rubbed onto a receiving surface) are now partof everyday life. They contain water-soluble or water-dispersiblesynthetic polymers of adhesive character dissolved in an aqueous organicliquid phase together with a shaping gel-form component. The gel-formingcomponent is selected in particular from alkali metal or ammonium saltsof aliphatic carboxylic acids, more particularly containing from about12 to 22 carbon atoms. If the basically high-tack water-basedpreparations of the synthetic polymers of adhesive character are heatedtogether with small quantities of the gel-forming component based onfatty acid soaps to relatively high temperatures, more particularlyabove 50° C., and if this solution is subsequently left standing tocool, the mixture solidifies to a more or less stiff soap gel in whichthe shaping and comparatively rigid micelle structure of the soap gel ispredominantly in evidence at first. This provides for the knownproduction and handling of such adhesives in stick form in closabletubes. When the stick is rubbed onto a receiving surface, the micellestructure is destroyed so that the rigid mixture is converted into apaste-like state in which its adhesive character is predominant.

Originally, the polyvinyl pyrrolidone (PVP) mentioned in DE 18 11 466proved to be the most important polymer of adhesive character. Althoughthe adhesive sticks made with polyvinyl pyrrolidone offered sufficientstrength for gluing paper, there was still a need to obtain sticks whichcould be used more universally and with which bonds of greater strengthcould be produced. In particular, there was a need to preventpaper/paper bonds established with the sticks from separating againunder climatically unfavorable conditions. The use of polyurethane asthe polymer of adhesive character contributed towards solving thatproblem.

EP 405 329 describes firm, soft-rubbing adhesive sticks based on a soapgel as the shaping gel-forming component and an aqueous poly-urethanedispersion as the adhesive component. The polyurethane is a reactionproduct of a polyol or a polyol mixture, a difunctional orpoly-functional isocyanate component, a component capable of saltformation in alkaline aqueous solution and/or a nonionic hydrophilicmodifying agent and, optionally, a chain-extending agent. Althoughimprovements were in fact obtained in this way, the strengths and heatresistance values were still not good enough for special cases.

SUMMARY OF THE INVENTION

Accordingly the problem addressed by the present invention was toprovide a dimensionally stable soft-rubbing composition which would nothave any of these disadvantages and which would be distinguished notonly by easy handling, but also by favorable performance properties. Inparticular, easy application would be combined with initialrepositionability of the bond and high tack would be combined with highultimate strength and also with high heat resistance.

The solution provided by the invention is defined in the claims andconsists essentially in the use of a mixture of polyurethane andpolyvinyl pyrrolidone as the synthetic polymer of adhesive character.

DETAILED DESCRIPTION OF THE INVENTION

The adhesive stick is “dimensionally stable” because its constituentcomposition is capable of forming stable geometric shapes at roomtemperature (20° C.). More particularly, an adhesive stick with adiameter of 16 mm should have a deformation load of 25 to 50 N asmeasured by the compressive strength method described hereinafter at atemperature of 20° C.

The constituent paste of the adhesive stick is preferably “soft-rubbing”because a uniform film without any unevenness is obtained on copyingpaper (Sonnecken 5015 Speziell Copier) under low pressure (see “rubbing”test).

An “water-based preparation” in the context of the invention isunderstood to be an aqueous mixture of the polymers irrespective of thedegree of dispersion (true solution, colloidal solution or dispersion).

The adhesive sticks according to the invention contain a polyurethane(PU) as the adhesive polymer component. The polyurethane is a reactionproduct of at least one polyol, at least one polyfunctional isocyanate,at least one component capable of salt formation in alkaline aqueoussolution and/or a nonionic hydrophilic modifying agent and, optionally,at least one chain-extending agent.

According to the invention, polyurethane dispersions are preferredstarting materials for adhesive sticks which are opaque, translucent ortransparent in appearance and in which the polymer would appear to bepresent at least partly in solution. The specialist knowledge of thepoly-urethane expert, who can influence the degree of distributionthrough the percentage content of ionic and/or nonionic constituents, isrelevant in this regard. Accordingly, the water-based preparationpreferably contains the polyurethane in the form of a dispersion.

The polyurethane dispersions used as synthetic polymer in adhesivesticks are prepared from a polyol or a polyol mixture as an essentialstarting product. Broadly speaking, these polyols should contain atleast two reactive hydrogen atoms and should be substantially linear,although they may also be branched. Their molecular weight is in therange from 300 to 40,000 and preferably in the range from 500 to 20,000.Suitable polyols are polyester polyols, polyacetal polyols, polyetherpolyols, polythioether polyols, polyamide polyols or polyester amidepolyols containing 2 to 4 hydroxyl groups which may also be partlyreplaced by amino groups. Polyurethanes of polyether and/or polyesterpolyols are preferred.

Suitable polyether polyols are, for example, the polymerization productsof ethylene oxide, propylene oxide, butylene oxide and theircopolymerization or graft polymerization products and the polyethersobtained by condensation of polyhydric alcohols or mixtures thereof andthose obtained by alkoxylation of polyhydric alcohols, amines,polyamines and aminoalcohols. Isotactic polypropylene glycol may also beused. The preferred polyether polyol is polytetrahydrofuran.Polytetrahydrofuran in the context of the present invention is thecollective name for polyethers which can be theoretically or actuallyprepared by ring-opening polymerization of tetrahydrofuran and whichcontain a hydroxyl group at either end of the chain. Suitable productshave a degree of oligomerization of about 1.5 to 150 and preferably inthe range from 5 to 100.

Another preferred class of polyols are polycarbonate polyols. Preferredpolycarbonate polyols are aliphatic types, i.e. esters of carbonic acidwith dihydric C₂₋₁₀ alcohols. Polycarbonate polyols based on carbonicacid and bisphenol A are less suitable.

Suitable polyacetal polyols are, for example, the compounds obtainablefrom glycols, such as diethylene glycol, triethylene glycol,4,4-dioxethoxydiphenyl dimethyl methane, hexanediol and formaldehyde.Suitable polyacetals may also be produced by polymerization of cyclicacetals.

Among the polythioether polyols, the condensation products ofthiodiglycol on its own and/or with other glycols, dicarboxylic acids,formaldehyde, aminocarboxylic acids or aminoalcohols are particularlysuitable. Depending on the co-components, the products arepolythioethers, polythio mixed ethers, polythioether esters,polythioether ester amides. Polyhydroxyl compounds such as these mayalso be used in alkylated form or in admixture with alkylating agents.

The polyester, polyester amide and polyamide polyols include thepredominantly linear condensates obtained from polybasic saturated andunsaturated carboxylic acids or anhydrides thereof and polyhydricsaturated and unsaturated alcohols, aminoalcohols, diamines, polyaminesand mixtures thereof and, for example, polyterephthalates orpolycarbonates. Polyesters of lactones, for example caprolactones, or ofhydroxycarboxylic acids may also be used. The polyesters may containterminal hydroxyl or carboxyl groups. Relatively high molecular weightpolymers or condensates such as, for example, polyethers, polyacetals orpolyoxymethylenes may also be used as alcohol component for theirsynthesis. The aqueous polyurethane dispersion preferably contains areaction product of a polyether and/or polyester polyol as polyolcomponent.

Polyhydroxyl compounds already containing urethane or urea groups andoptionally modified natural polyols, such as castor oil, may also beused. Basically, polyhydroxyl compounds containing basic nitrogen atoms,for example polyalkoxylated primary amines or polyesters orpolythioethers containing co-condensed alkyl diethanolamine, are alsosuitable. Polyols obtained by complete or partial ring opening ofepoxidized triglycerides with primary or secondary hydroxyl compounds,for example the reaction product of epoxidized soybean oil withmethanol, may also be used. The polyols may also contain aminoalcoholsor diamines.

Polyisocyanates suitable for the production of the polyurethanes usablein accordance with the invention are any aromatic and aliphaticdiisocyanates such as, for example, 1,5-naphthylene diisocyanate,4,4′-diphenyl methane diisocyanate, 4,4′-diphenyl dimethyl methanediisocyanate, di- and tetraalkyl diphenyl methane diisocyanate,4,4′-dibenzyl diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylenediisocyanate, the isomers of toluene diisocyanate, optionally inadmixture, 1-methyl-2,4-diisocyanatocyclohexane,1,6-disocyanato-2,2,4-trimethyl hexane, 1,6-diisocyanato-2,4,4-trimethylhexane, 1-isocyanatomethyl-3-isocyanato-1,5,5-trimethyl cyclohexane,chlorinated and brominated diisocyanates, phosphorus-containingdiisocyanates, 4,4′-diisocyanatophenyl perfluoroethane,tetramethoxybutane-1,4-diisocyanate, butane-1,4-disocyanate,hexane-1,6-disocyanate, dicyclohexylmethane diisocyanate,cyclohexane-1,4-diisocyanate, ethylene diisocyanate, phthalicacid-bis-isocyanatoethyl ester, also polyisocyanates containing reactivehalogen atoms, such as 1-chloromethylphenyl-2,4-diisocyanate,1-bromomethylphenyl-2,6-diisocyanate,3,3-bis-chloromethylether-4,4′-diphenyl diisocyanate. Sulfur-containingpolyisocyanates are obtained, for example, by reacting 2 moles ofhexamethylene diisocyanate with 1 mole of thiodiglycol ordihydroxydihexyl sulfide. Other important diisocyanates are trimethylhexamethylene diisocyanate, 1,4-diisocyantobutane,1,2-diisocyanatododecane and dimer fatty acid diisocyanate. Theisocyanates mentioned above may be used either individually or in theform of mixtures. Preferred isocyanates are cyclic or branched aliphaticdiisocyanates, such as isophorone diisocyanate, but also hexamethylenediisocyanate. Tetramethyl xylene diisocyanate (TMXDI) is particularlypreferred. Trifunctional isocyanates may also be used in smallquantities. The aqueous polyurethane dispersion is preferably a reactionproduct of at least one difunctional or trifunctional aliphaticisocyanate.

Chain-extending agents containing reactive hydrogen may also be used inthe production of the polyurethane dispersions used in accordance withthe invention.

Suitable chain-extending agents containing reactive hydrogen atomsinclude:

the usual saturated and unsaturated glycols, such as ethylene glycol orcondensates of ethylene glycol, butane-1,3-diol, butane-1,4-diol,butenediol, propane-1,2-diol, propane-1,3-diol, neopentyl glycol,hexanediol, bis-hydroxymethyl cyclohexane, dioxyethoxyhydroquinone,terephthalic acid-bis-glycol ester, succinic acid di-2-hydroxyethylamide, succinic acid di-N-methyl-(2-hydroxyethyl)-amide1,4-di-(2-hydroxymethylmercapto)-2,3,5,6-tetrachlorobenzene,2-methylpropane-1,3-diol, 2-methylpropane-1,3-diol;

aliphatic, cycloaliphatic and aromatic diamines, such as ethylenediamine, hexamethylene diamine, 1,4-cyclohexylene diamine, benzidine,diaminodiphenyl methane, dichlorodiaminodiphenyl methane, the isomers ofphenyl diamine, hydrazine, ammonia, carbohydrazide, adipic aciddihydrazide, sebacic acid dihydrazide, piperazine, N-methyl propylenediamine, diaminodiphenyl sulfone, diaminodiphenyl ether, diaminodiphenyldimethyl methane, 2,4-diamino-6-phenyl triazine;

aminoalcohols, such as ethanolamine, propanolamine, butanolamine,N-methyl ethanolamine, N-methyl isopropanolamine;

aliphatic, cycloaliphatic, aromatic and heterocyclic mono- anddiaminocarboxylic acids, such as glycine, 1- and 2-alanine,6-aminocaproic acid, 4-aminobutyric acid, the isomeric mono- anddiaminobenzoic acids, the isomeric mono- and diaminonaphthoic acids;

water.

The polyols used as chain-extending agents preferably have a molecularweight of less than 300. It is emphasized that it is not possible in thecontext of the present invention strictly to differentiate between thepolyols having a molecular weight of 300 to 20,000 and the so-called“chain-extending agents” because the transitions between the two classesof compounds are fluid. Compounds which are not made up of severalmonomer units, but have a molecular weight of more than 300, such as3,3′-dibromo4,4′-diaminodiphenyl methane for example, are classed aschain-extending agents, as indeed is pentaethylene glycol although, onthe strength of its composition, pentaethylene glycol is actually apolyether diol.

Special chain-extending agents containing at least one basic nitrogenatom are, for example, mono-, bis- or polyalkoxylated aliphatic,cycloaliphatic, aromatic or heterocyclic primary amines, such asN-methyl diethanolamine, N-ethyl diethanolamine, N-propyldiethanolamine, N-isopropyl diethanolamine, N-butyl diethanolamine,N-isobutyl diethanolamine, N-oleyl diethanolamine, N-stearyldiethanolamine, ethoxylated cocofatty amine, N-allyl diethanolamine,N-methyl diisopropanolamine, N-ethyl diisopropanolamine, N-propyldiisopropanolamine, N-butyl diisopropanolamine, C-cyclohexyldiisopropanolamine, N,N-diethoxylaniline, N,N-diethoxyltoluidine,N,N-diethoxyl-1-aminopyridine, N,N′-diethoxylpiperazine,dimethyl-bis-ethoxylhydrazine, N,N′-bis-(2-hydroxyethyl)-N,N′-diethylhexahydro-p-phenylene diamine, N-12-hydroxyethyl piperazine,polyalkoxylated amines, such as propoxylated methyl diethanolamine, alsosuch compounds as N-methyl-N,N-bis-3-aminopropyl amine,N-(3-aminopropyl)-N,N′-dimethyl ethylene diamine,N-(3-aminopropyl)-N-methyl ethanolamine,N,N′-bis-(3-aminopropyl)-N,N′-dimethyl ethylene diamine,N,N′-bis-(3-aminopropyl)-piperazine, N-(2-aminoethyl)-piperazine,N,N′-bis-hydroxyethyl propylene diamine, 2,6-diaminopyridine,diethanolaminoacetamide, diethanolamidopropionamide,N,N-bis-hydroxyethyl phenyl thiosemicarbazide, N,N-bis-hydroxyethylmethyl semicarbazide, p,p′-bis-aminomethyl dibenzyl methyl amine,2,6-diaminopyridine, 2-dimethylaminomethyl-2-methylpropane-1,3-diol.

In addition, the polyurethanes on which the polyurethane dispersionsused in accordance with the invention are based contain awater-solubilizing functional component as an important component. Thiscomponent may be selected from dihydroxy or even diamino compoundscontaining an ionizable carboxylic acid, sulfonic acid, amino orammonium group. These compounds may either be used as such or may beprepared in situ. In order to introduce compounds bearing ionizablecarboxylic acid groups into the polyurethane, the expert may add adihydroxycarboxylic acid capable of salt formation to the polyols. Apreferred dihydroxycarboxylic acid is, for example, dimethylol propionicacid.

In order to introduce sulfonic acid groups capable of salt formation, adiaminosulfonic acid may be added to the polyols. Examples are2,4-diaminobenzenesulfonic acid and also theN-(ω-aminoalkane)-ω′-aminoalkanesulfonic acid described in DE 20 35 732.If they are anionically modified, the polymers are present in thepolyurethane dispersions used in accordance with the invention in saltform. In the case of the preferred polymers modified with carboxylicacids or sulfonic acids, alkali metal salts, ammonia or amines, i.e.primary, secondary or tertiary amines, are present as counterions.

According to the invention, the neutralizing agents are preferably usedin a stoichiometric ratio or in excess, based on acid groups.

Accordingly, the groups capable of salt formation may be partly orcompletely neutralized by the counterions. An excess of neutralizingagent is also possible.

In addition to or instead of the preferred modification with componentscapable of salt formation, nonionic modification can also inducesolubility in water. Monoalcohols obtained by reaction of primaryalcohols with ethylene oxide are primarily suitable for the nonionicmodification. The necessary quantities of nonionic modifying agents isdetermined by the hydrophilicity of the system as a whole, i.e. it islower where polyethylene glycol-based polyols have already been used aspolyols in the synthesis of the polymer. The quantity is of course alsolower when ionic groups are additionally incorporated. The upper limitis determined by the water resistance of the adhesive film. For example,up to 85% by weight of the polyurethane, based on the solid, mayoriginate from ethylene oxide. In the absence of ionic modification,typical values are 5 to 50% by weight. Where ionic modifying agents areused, however, lower values may also be adjusted.

In addition, monohydric alcohols, more particularly ether alcohols, mayadditionally be used as nonionic hydrophilic modifying agents. Thereaction products of C₁₋₁₀ alcohols with ethylene oxide in the molecularweight range up to 20,000 and preferably from 200 to 6,000 arepreferred.

To produce the polyurethanes particularly suitable for the purposesaccording to the invention, the polyols and an excess of diisocyanateare reacted to form a polymer terminated by isocyanate groups, suitablereaction conditions and reaction times and also temperatures beingvariable according to the particular isocyanate. The expert knows thatthe reactivity of the constituents to be reacted necessitates acorresponding balance between the reaction rate and unwanted secondaryreactions which can lead to discoloration and a reduction in molecularweight. Typically, the reaction is carried out with stirring over aperiod of about 1 to 6 hours at a temperature of approximately 50 toapproximately 120° C. Further particulars of the production of suitablepolyurethanes can be found in EP 405 329, to which is reference isexpressly made.

However, the polyurethane dispersions used in the adhesive sticksaccording to the invention may also be produced without using acetone asa solvent. In this case, the starting materials may be the polyolspreferred for the purposes of the invention based on polytetrahydrofuranor its copolymers with ethylene oxide or propylene oxide, low molecularweight polyols, for example those with a molecular weight of up to 2,000or up to 1,000, preferably being used. The polyols are then reacted inthe presence of a polyol bearing acid groups, i.e. for exampledimethylol propionic acid, in an OH:NCO ratio of greater than 1:1.2 toform stirrable resins which may then be directly dispersed in water.

Clear or opaque polyurethane dispersions are preferably used for thepurposes of the invention. In order to obtain substantially clear, i.e.transparent, opaque or water-clear polyurethane dispersions, it isimportant to maintain a certain ratio between the component capable ofsalt formation and the other components involved in the synthesis of thepolyurethane. Thus, the component capable of salt formation, expressedas dimethylol propionic acid, is used in quantities of 1 to 30% byweight, preferably 2 to 20% by weight and more preferably 10 to 18% byweight, based on polyol. Based on polyurethane solids and expressed asdimethylol propionic acid, this corresponds to 5 to 35% by weight,preferably 5 to 20% by weight and more preferably 5 to 15% by weight. Inaddition, the transparency depends on the degree of neutralization. Theexpert is able by carrying out a few preliminary tests to determine thequantity of modifying agent capable of ion formation or the quantity ofneutralizing agent beyond which an adequate degree of transparency isachieved. In general, as little of these substances as possible will beused because excessive use can affect the water resistance of theadhesive film.

An important factor in the production of the polyurethane dispersions onwhich the adhesive sticks according to the invention are based is theratio of hydroxyl groups to isocyanate groups which may be between1.0:0.8 and 1.0:4.0. Ratios of 1.0:1.1 to 1.0:2.0 are preferred, ratiosof 1.0:1.1 to 1.0:1.8 being particularly preferred. Aqueous polyurethanedispersions with these ratios are particularly appropriate when they area reaction product of a polyol mixture, a component capable of saltformation in alkaline solution and a polyisocyanate.

Suitable polyurethane dispersions may be prepared over a broadconcentration range. Preparations with a solids content of 20 to 80% byweight are preferred, those with a solids content of 30 to 60% by weightbeing particularly preferred.

The polyurethane should make up from 10 to 60% by weight and, moreparticularly, from 15 to 35% by weight of the adhesive stick as a whole,based on the total weight of the polymers, the soap and otherauxiliaries and water.

According to the invention, polyvinyl pyrrolidone (PVP) is used as asecond polymer of adhesive character. It should have a molecular weightof at least about 10,000, more particularly of about 50,000 to 3,000,000and, above all, of about 400,000 to 1.5 million. The PVP should be addedin a quantity of 0.5 to 30% by weight and preferably in a quantity of 1to 15% by weight, based on the adhesive as a whole. The percentagecontent of both adhesive polymers together should be between 15 and 65%by weight and preferably between 18 and 35% by weight.

The adhesive sticks according to the invention contain alkali metalsalts, more particularly sodium salts, of C₁₂₋₂₂ fatty acids of naturalor synthetic origin as soaps for forming the gel structure. C₁₄₋₁₈ fattyacid mixtures are preferred. The sodium salts of the fatty acids, i.e.the soaps, are present in quantities of 2 to 20% by weight andpreferably 3 to 12% by weight, based on the adhesive stick.

The auxiliaries typically used in adhesive sticks may also be used inthe adhesive sticks according to the invention in quantities of 0 to 25%by weight, based on the adhesive stick. The auxiliaries in question are,in particular, water-soluble plasticizers, dyes, perfumes, resins,preservatives and/or moisture regulators.

However, plasticizers and/or moisture regulators, i.e. organicwater-soluble solvents typically used in adhesive sticks, are preferablynot used for the purposes of the present invention. Nevertheless, thesecompounds may optionally be present in small quantities. The compoundsin question are polyglycol ethers, more particularly polyethylene glycoland polypropylene glycol, the preferred polyethers having an averagemolecular weight in the range from 200 to 4,000 and preferably in therange from 500 to 2,000. In addition, polyhydric alcohols, such asglycerol, trimethylol propane, propylene glycol, sorbitol, sugar,polyglycerol, low molecular weight starch hydrolyzates and/or polyetherglycols, may also be used. For example, a mixture of glycerol andpolyethylene glycol may optionally be used. The non-volatile organicsolvents mentioned should be used in quantities of at most up to 50% byweight, based on the water content of the sticks.

In addition, other auxiliaries, for example substances which promoteeasy and soft rubbing, may also be used. Substances such as these are,for example, aminocarboxylic acids and/or their lactams. Suitableaminocarboxylic acids or lactams should contain up to 12 carbon atomsand more particularly from 4 to 8 carbon atoms. The preferredrepresentative in terms of practical application is ε-caprolactam or the7-aminocaproic acid derived therefrom. The quantity in which the lactamsor corresponding aminocarboxylic acids are used is normally no more than15% by weight and, for example, between 1% by weight and 10% by weight,based on the stick as a whole.

The adhesive sticks according to the invention may contain pigments,dyes, antioxidants, bitter substances, fillers, fragrances,preservatives, resins, water-soluble plasticizers and/or moistureregulators as further auxiliaries. These auxiliaries are present in theusual small quantities of 0 to about 20%, based on the adhesive stick asa whole. Examples of special dyes are pH- and heat-dependent dyes,optical brighteners, dyes designed to change color on application,particularly in the functional range. The dye may be uniformlydistributed in the adhesive. However, structured coloration, for examplea core/jacket structure, is also possible. Examples of pigments orfillers are graphite, talcum, TiO₂, highly disperse silica (Aerosil),bentonite, wollastonite, chalk, magnesium oxide and glass fibers. Otherpossible additives are, for example, dextrins, cellulose derivatives andnon-destructured starch derivatives. Other additives which may bepresent in the adhesive sticks according to the invention are mannans,more particularly galactomannans. Galactomannans from the fruit of thecarob tree and from guar flour are particularly suitable. Thedestructured ethers may also be replaced to a small extent bydestructured mannans.

The individual components are preferably present in the adhesive stickin the following quantities: 3 to 10% by weight soaps, 15 to 65% byweight PU or PVP polymers and 0 to 25% by weight auxiliaries. Thebalance to 100% is water. Water is preferably present in a quantity of35 to 65% by weight and more preferably 40 to 55% by weight, based onthe adhesive stick as a whole.

To produce the adhesive sticks according to the invention, thesoap-gel-forming constituents, the polyurethane dispersion, the PVP andthe auxiliaries are mixed together, heated to temperatures of at least50° C. and preferably up to 100° C. (or boiling point) until a uniformmixture is formed, the resulting mixture is poured into molds and isthen left to cool in the absence of mechanical action to form a gel.These mixtures, which are easy to pour in the temperature rangementioned, are preferably poured directly into molds, more particularlyinto stick tubes or similar containers, and left to solidify in theabsence of mechanical action to form the required gels. The adhesivestick is stored in a closable tube, more particularly of polyolefin.Although the tack is very high, the adhesive stick is displaceable inthe tube.

Accordingly, the adhesive composition according to the invention is veryeasy to convert into stick form in the very tubes in which it will laterbe handled. This method of shaping is so simple that, after the originaladhesive stick has been used up, anybody can make an easy-to-handlestick in the old tube simply by heating another adhesive compositionaccording to the invention and pouring it into the stick tubes. In otherwords, the tube is reusable.

Since the adhesive stick according to the invention is solid andsoft-rubbing, it is preferably used in geometric, more particularlycylindrical, form. The cylinder may have a circular, oval or polygonalcross-section. Its dimensions will be determined by the application, forexample by the required width of the surface to be covered. Squareblocks are also possible. The most appropriate form is determined by theapplication of the adhesive composition to the substrate.

The adhesive sticks according to the invention have the advantage ofrelatively high adhesive strength and, accordingly, may be used not onlyfor gluing paper, but also and in particular paperboard, wall coverings,leather, wood, wood materials, plastics, glass, metals, ceramics,gypsum, to materials of the same or different kinds, more particularlyfor absorbent woods of other substrates, such as paperboard, even incombination with PVC, PMMA, PBS, aluminium.

By virtue of its high adhesive strength on many different substrates,the adhesive stick may be used as a “multipurpose adhesive”, especiallysince its application from the tube is simple and uniform. Specificexamples include handicrafts where the strengths of a conventionaladhesive stick are unsatisfactory, such as the bonding of foam rubber topaperboard or wood. By virtue of its high heat resistance, the adhesivestick according to the invention is suitable for example for gluingwindow posters directly exposed to sunlight.

Although the PU and the PVP are soluble or dispersible in water, thewater resistance of the bond is considerable. Thus, 20% of the originaladhesive strength is present, for example, in a humid climate of 30°C./80% relative air humidity.

Mistakes and adhesive residues can easily be removed with alkaline waterby covering the affected areas with a damp cloth for 10 minutes tosoften the adhesive and then wiping off the remains.

The adhesive composition according to the invention sets relativelyquickly by comparison with standard multipurpose adhesives, for exampleon wood/PVC. However, enough time remains for correction. The open timeis between 10 and 120 seconds and preferably between 20 and 60 seconds.

The stick form is particularly convenient where the solid, soft-rubbingadhesive composition according to the invention is to be applied byhand. Other applications may be better served by other forms, forexample a square form, where relatively large areas are to be coated bymachine.

EXAMPLES

I. Starting Materials

1. Preparation of the Polyurethane Solutions or Dispersions

The polyurethane adhesive raw materials are produced by the acetoneprocess, although other methods, for example dispersion of the extrudedprepolymer melt (melt extrusion process), are possible. Thepolyisocyanates and diol components (polyether diol and dimethylolpropionic acid) are introduced first and stirred under reflux at around65 to 100° C. until the NCO value is constant. On completion of thereaction, the quantity of water indicated, which contains the calculatedquantities of alkali and any chain extender, is added with vigorousstirring. Intensive shearing is very important to the quality andespecially to the homogeneity of the dispersion. After stirring forseveral hours, the solvent is distilled off until the acetoneconcentration is well below 0.1 and the viscosities and solids contentsshown in Table I below are reached.

2. A PVP with a K value of 90 (manufacturer: ISP) was used.

3. ε-Caprolactam.

4. Sodium palmitate (Henkel KGaA).

TABLE I Polyurethane No. I Parts by weight water 1363 Parts by weightTMXDI 242 Parts by weight polypropylene glycol (MW 400) 40 Parts byweight polypropylene glycol (MW 1000) 300 Parts by weightpolytetrahydrofuran (MW 850) 65 Parts by weight dimethylol propionicacid 67 Parts by weight NaOH (100%) 20 Solids content (%) 35 Viscosityat 20° C. (mPas) 3500

II. Production of the Stick Compositions

The stick compositions are obtained by mixing the individual componentsin Table II at 65 to 100° C. and then pouring them into stick tubes tocool, the pH of the composition optionally being adjusted to a value of8 to 11 by addition of a little dilute sodium hydroxide.

TABLE II Ingredient/ Properties Example 1 Example 2 Example 3 Example 4PU dispersion 91 88 85 0 35% solids, % by weight PVP, % by weight 0 3 626 + 65 water ε-Caprolactam, % by 1 1 1 1 weight Na palmitate 8 8 8 8Tensile shear strengths 3 4 5.5 1.5 on beech/beech MPa Beech/PVC in MPa2.2 3.3 5.2 1.3 Open time 10 20 40 10 Setting time (secs.) 10 15 15 10Heat resistance ° C. 55 75 100 100 Tack Medium Good Very good Very poor

III. Tests

1) Compressive Strength

Compressive strength is understood to be the maxmimum load measuredparallel to the longitudinal axis on collapse of the stick underpressure. Compressive strength is measured with an Erichsen Model 464Lcompressive strength tester, measuring head 709 (manufacturer: Erichsen,Simonshöfchen, Wuppertal).

The adhesive cut off with a minimum length of 30 mm immediately abovethe piston is placed between two holders in the form of approx. 10 mmthick disks of rigid PVC which are formed with a circular 3 mm deepdepression adapted to the particular stick diameters. The stick providedwith the holders is placed centrally on the table of the compressivestrength tester. The height of the force measuring instrument over thetable is adapted to the height of the stick to be tested. The measuringhead is then advanced against the stick to be tested at a rate ofapprox. 70 mm per minutes. On reaching the maximum compressive force,the value is read off from the digital display. The adhesive sticksaccording to the invention have a compressive strength of about 25 to 50N/16 mm diameter.

2) Setting Time

To determine whether the adhesive properties of the sticks aresufficient for the application envisaged, bonding tests are carried outby hand under certain processing conditions and evaluated. The followingprocedure is adopted:

A supply of white chrome paper (weight per unit area approx. 100 g/m²)coated on one side and adhesive sticks to be tested are conditioned forat least 24 hours at 20° C./65% relative air humidity. The test paper iscut into strips 5 cm wide and approx. 30 cm long. An adhesive stick isrubbed twice longitudinally under uniform pressure over the uncoatedside of a paper strip and should produce a uniform film. Immediatelyafterwards, a second paper strip which has not been coated with adhesiveis placed on the coated strip with its uncoated side facing inwards andrubbed on by hand. An attempt is then made to peel the paper stripsslowly from one another. The time at which separation in the adhesionzone is only possible with tearing of paper over entire widthcharacterizes the setting time.

3) Open Time

The open time is the time after application of the adhesive within whichthe materials to be bonded have to be fitted together in order, aftersetting, to obtain complete tearing of paper in the separation test. Themethod is the same as that used to determine setting time except thatthe strips of paper are only fitted together after defined timesfollowing application of the adhesive. Beginning with 15 seconds, theopen time may be graduated, for example, in intervals of 15 seconds.With slow-setting adhesives having predictably longer open times,correspondingly longer intervals will be selected.

4) Rubbing

Rubbing is subjectively evaluated by at least two examiners. Theperformance properties are characterized and classified as follows:smooth, pliable, flat, crumbly, greasy, hard, soft and stringy.

5) Tensile Shear Strength of Wood/Wood Bonds

Beech wood test specimens and the PVC test specimens are rubbed withadhesive at their ends and fitted together in such a way that the twoadhesive-covered ends overlap by 2 cm (bond area 2 cm×2.5 cm). The testspecimens are fixed with two clamps and measured after 24 hours. Theresult is expressed in N/mm².

6) Heat Resistance

For preparation of the bonds, see testing of tensile shear strength. Thepressure applied is 1.0 N/mm².

When ultimate strength has been developed after about 3 to 5 days atroom temperature, the test specimens are hung up in a heating cabinet. Aload of 1 kg is then applied to the bond. The heating cabinet increasesthe temperature in stages from 30° C. to 120° C. over a period of 30hours. Standard program: 30° C. to 120° C. in 30 h, 10° C. temperatureincrease every 3 h. If the bond holds the weight for the entire durationof the program, the load is increased first to 2 kg and then to 5 kg.Each measurement is carried out on at least three bonds per adhesive.

The heat resistance of the adhesive is determined by comparing themeasured time with the Table:

H 0-3.0 3-6 6-9 9-12 12-15 15-18 18-21 21-24 24-27 27-30 ° C. 30° C. 40°C. 50° C. 60° C. 70° C. 80° C. 90° C. 100° C. 110° C. 120° C.

7) Tack

The test is carried out in a standard climate of 23° C./50% relative airhumidity using test specimens of beech plywood stored therein for atleast 3 days.

Two wood test specimens measuring 80 mm×25 mm×4 mm are coated with theparticular adhesive with a 20 mm long overlap corresponding to anoverlap area of 500 mm², pressed together for 5 seconds under a pressureof 0.2 N/mm² and subjected to a shear force of 200 g immediately andafter 2, 4, 6 and 8 mins. The test counts as having been passed if theparts no longer slide relative to one another after an hour.

Depending on the time required, tack is evaluated on the followingscale:

very good immediately (0 mins.) good between 0 and 2 mins. averagebetween 2 and 4 mins. poor between 4 and 6 mins very poor more than 6mins.

The test results (see Table II) show that the adhesive compositionaccording to the invention based on the combination of both polymersleads to better tack and to higher heat resistance than the individualpolymers on their own.

What is claimed is:
 1. An adhesive stick comprised of (a) a shapinggel-forming substance comprised of a soap; and (b) a water-basedpreparation comprising polyurethane, which is a reaction product of oneor more polyols having a molecular weight of 300 to 40,000 and one ormore polyfunctional isocyanates, and polyvinyl pyrrolidone having amolecular weight greater than 400,000.
 2. The adhesive stick of claim 1wherein said polyurethane is in the form of a dispersion.
 3. Theadhesive stick of claim 1 wherein said polyurethane is a reactionproduct of at least one such polyol, at least one polyfunctionalisocyanate, and one or more components selected from the groupconsisting of components capable of salt formation in alkaline aqueoussolution and nonionic hydrophilic modifying agents.
 4. The adhesivestick of claim 3 wherein at least one chain-extending agent isadditionally used to produce said polyurethane.
 5. The adhesive stick ofclaim 1 wherein said polyurethane is in the form of an aqueousdispersion and is a reaction product of (a) a mixture of such polyols(b) a component capable of salt formation in an alkaline aqueoussolution and (c) a polyisocyanate in an OH:NCO ratio of 1.00:8 to1.0.4.0.
 6. The adhesive stick of claim 5 wherein the OH:NCO ratio is1.0:1.1 to 1.0:2.0.
 7. The adhesive stick of claim 5 wherein the OH:NCOratio is 1.0:1.1 to 1.0:1.8.
 8. The adhesive stick of claim 3 whereinthe polyol is selected from the group consisting of polyether polyols,polyester polyols, and mixtures thereof.
 9. The adhesive stick of claim3 wherein at least one of said components is a dihydroxy carboxylic acidcapable of salt formation in alkaline aqueous solution.
 10. The adhesivestick of claim 3 wherein at least one polyfunctional isocyanate isselected from the group consisting of difunctional aliphaticisocyanates, trifunctional aliphatic isocyanates, and mixtures thereof.11. The adhesive stick of claim 1 wherein the polyvinyl pyrrolidone hasa molecular weight of up to 1.5 million.
 12. The adhesive stick of claim1 wherein said soap is comprised of sodium salts of C₁₂₋C₂₂ fatty acids.13. The adhesive stick of claim 1 additionally comprising one or moreauxiliaries selected from the group consisting of water-solubleplasticizers, dyes, resins, preservatives, moisture regulators andmixtures thereof.
 14. An adhesive stick comprised of (a) a shapinggel-forming substance comprised of sodium salts of C₁₂₋C₂₂ fatty acids,(b) a water-based preparation comprising (i) a dispersed polyurethanewhich is a reaction product of one or more polyols having a molecularweight of 300 to 40,000, at least one polyfunctional isocyanate, and acomponent capable of salt formation in alkaline aqueous solution in anOH:NCO ratio of 1.0:0.8 to 1.0:4.0; and (ii) a polyvinyl pyrrolidonehaving a molecular weight greater than 400,000.
 15. The adhesive stickof claim 14 wherein the component capable of salt formation is selectedfrom the group consisting of dihydroxy and diamino compounds containingat least one ionizable carboxylic acid, sulfonic acid, amino or ammoniumgroup.
 16. The adhesive stick of claim 14 wherein the dispersedpolyurethane has a solids content of 30 to 60% by weight.
 17. Theadhesive stick of claim 14 wherein the polyurethane of the polyurethanedispersion comprises from 15% to 35% by weight of the adhesive stick.18. The adhesive stick of claim 14 wherein the polyvinyl pyrrolidone hasa molecular weight of up to 1.5 million.
 19. The adhesive stick of claim14 wherein the polyvinyl pyrrolidone comprises from 1% to 15% by weightof the adhesive stick.
 20. The adhesive stick of claim 14 wherein thesodium salts of C₁₂₋C₂₂ fatty acids comprise 3 to 12% by weight of theadhesive stick.
 21. The adhesive stick of claim 14 additionallycomprising at least one amino carboxylic acid or lactam.
 22. A method ofmaking an adhesive stick comprising the steps of: (a) mixing together asoap, a polyurethane dispersion which is a reaction product of one ormore polyols having a molecular weight of 300 to 40,000, at least onepolyfunctional isocyanate, and a polyvinyl pyrrolidone having amolecular weight greater than 400,000 to form a mixture; (b) heatingsaid mixture at a temperature of at least 50° C. for a time effective torender said mixture uniform; (c) pouring said uniform mixture into amold; and (d) cooling the uniform mixture in the mold without anymechanical action until a gel is formed.
 23. A method for bonding afirst material to a second material, wherein the adhesive stick of claim1 is used to bond said first material to said second material.
 24. Amethod for bonding a first material to a second material, said firstmaterial and second material being independently selected from the groupconsisting of paper, paperboard, wood, foam rubber, gypsum, leather,plastic, ceramic and glass, wherein the adhesive stick of claim 14 isrubbed onto said first material to coat the first material with adhesiveand said adhesive coated on said first material is used to bond saidfirst material to said second material.